FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] This gene encodes a mitogen-responsive phosphoprotein. It is expressed in normal ovarian epithelial cells, but is down-regulated or absent from ovarian carcinoma cell lines, suggesting its role as a tumor suppressor. This protein binds to the SH3 domains of GRB2, an adaptor protein that couples tyrosine kinase receptors to SOS (a guanine nucleotide exchange factor for Ras), via its C-terminal proline-rich sequences, and may thus modulate growth factor/Ras pathways by competing with SOS for binding to GRB2. Alternatively spliced transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Oct 2011] PHENOTYPE: Homozygous null mutants exhibit abnormal primitive endoderm structure and/or function, lack a proamniotic cavity and die prior to embryonic day 9.5. A conditional mutant survives, but shows kidney proximal tubule abnormality. [provided by MGI curators]